At present, with the rapid development of Wireless Local Area Network (WLAN), the demand for the coverage of the WLAN is growing in the field of wireless networks. The most common WLAN technologies for a series of standards, such as 802.11a, 802.11b and 802.11g are defined in the Institute of Electrical and Electronic Engineers (IEEE) 802.11 group; since then, other task groups appear successively to devote to the development of the specification referring to the improvement of conventional 802.11 technology, for example, the 802.11n task group sets a High Throughput (HT) requirement and supports a data rate as high as 600 Mbps; and the 802.11ac task group further puts forward the concept of Very High Throughput (VHT) to increase the data rate to 1 Gbps. A new protocol needs to be backward compatible with the previous protocols.
In 802.11, an Access Point (AP) and a plurality of non-APs associated with the AP make up a Basic Service Set (BSS), as shown in FIG. 1. The WLAN defined by IEEE802.11 uses the Carrier Sense Multiple Access (CSMA) mechanism with Collision Avoidance (CA) to enable multiple points to share a wireless channel.
In IEEE802.11 technology, a channelized set refers to a set consisting of multiple channels of 20 MHz defined from a predefined or fixed start frequency and multiple broadband channels consisting of these channels of 20 MHz in a given frequency band. These channels of 20 MHz making up the set are also called basic channels and other channels consisting of these basic channels are also called broadband channels. A broadband channel includes a basic channel called a main channel, which is used for broadcasting control information. In a channelized set, each basic channel has a unique channel number.
In the description of the disclosure, available channels refer to a group of non-overlapped basic channels defined in a channelized set or the set of these basic channels; and a working channel refers to an available channel being used or to be used by a wireless device.
In the technology defined by a series of standards of IEEE802.11, a license-free ISM frequency band is channelized into multiple channels of 20 MHz according to the basic channel bandwidth of 20 MHz. An interval of 5 MHz exists between adjacent channel center frequencies; and the channels are numbered according to a given or predefined start frequency. Multiple channels defined above are taken as working channels in IEEE802.11. For example, in a frequency band of 2.4 GHz, fourteen adjacent channels of 20 MHz are defined in IEEE802.11 to serve as available channels; and these available channels and their adjacent available channel have a 5 MHz interval in terms of center frequency, and are overlapped with one another. For another example, in a frequency band of 5 GHz, five channels of 20 MHz between 5.735 GHz and 5.835 GHz are defined in IEEE802.11 to serve as available channels; and these available channels and their adjacent available channel have a 20 MHz interval in terms of center frequency and are not overlapped with one another.
In some cases, the frequency planning of some countries cannot be fully utilized under the definition of channelization. For example, in a frequency band of 5 GHz in China, a frequency band of 125 MHz in total between 5.725 GHz to 5.850 GHz can be used for the WLAN, and the frequency band can be divided into six available channels of 20 MHz, or a signal of 120 MHz bandwidth can be defined by a more effective channelization scheme. Whereas, a problem of center frequency deviation exists between the more effective channelization scheme and the conventional 5 GHz channelization scheme, so that the WLAN equipment cannot perform simple expansion processing on the efficient channelization scheme according to the conventional channelization scheme; and particularly, devices cannot communicate with each other in the conventional way when working in a WLAN according to different channelization schemes. In such case, multiple working modes may coexist, wherein the working mode refers to that a data transmission signal is transmitted by a channel defined by a channelized set and a corresponding bandwidth, or a frame exchange sequence is transmitted by a channel defined by one or more channelized sets and a corresponding bandwidth. The frame exchange sequence refers to the sending of a series of wireless frames and corresponding wireless frame feedback required to complete one data transmission. For example, generally, a transmitted data frame may follow an acknowledgement frame from a receiver; and before a long data frame is sent, a receiver and a sender may exchange two short wireless frames to reserve a channel to send the data frame subsequently.
Therefore, how to design a more effective channelization scheme compatible with the conventional channelization scheme and provide a method for switching between different working modes is a problem to be solved in a new generation of broadband-based 802.11 protocol.